Heat-shock cognate protein 70 (Hsc70), a molecular chaperone constitutively expressed in the cell, is involved in the regulation of several cellular signaling pathways. In this study, we found that TGF-beta-induced phosphorylation and nuclear translocation of Smad2/3 were suppressed in fibroblastic NRK-49F cells treated with small interfering RNA (siRNA) for Hsc70. In the cells underexpressing Hsc70, transcriptional induction of connective tissue growth factor (CTGF), a target gene of the TGF-beta signaling, was also suppressed in the early phase of TGF-beta stimulation. Upon stimulation with TGF-beta, Hsc70 interacted with Smad2/3, suggesting functional interactions of Hsc70 and Smad2/3 for the activation of TGF-beta-induced Smad signaling. Although the expression of heat-shock protein 70 (Hsp70) was upregulated in the cells treated with Hsc70 siRNA, TGF-beta-induced Smad activation was not affected in the cells over expressing Hsp70. Collectively, these results indicate that Hsc70, but not Hsp70, supportively regulates TGF-beta-induced Smad signaling in NRK-49F cells. (C) 2016 Elsevier Inc. All rights reserved.